This invention relates to the field of emergency power sources. More particularly, the invention relates to a so-called UPS (uninterrupted power supply) system.
UPS systems are used as a sort of buffer between ordinary commercial alternating-current (AC) utility power and critical components such as computers, so that if the line voltage varies or is interrupted, power to the load is maintained at adequate levels or is not lost. The traditional UPS system is typically comprised of a rectifier, inverter and battery charger. It may be explained here, that in order to eliminate shock hazards, it is required that the neutral line or conductor from ordinary commercial AC utility power be grounded. Because of the inherent nature and mode of operation of typical UPS systems, the integrity of the neutral is destroyed as the AC power is processed by the UPS. In a typical UPS system, AC power supplied to the UPS is full-wave rectified which destroys the integrity of the neutral conductor. In order to re-establish the integrity of the neutral conductor, some type of isolation means is required in the UPS system. Typically such isolation means takes the form of a 50 or 60 Hz transformer.
With the increasingly widespread development and use of smaller, less expensive computers, there has been an increasing emphasis on the development of smaller and less expensive UPS systems. A significant contributor to the overall cost, weight and size of UPS systems is the 50 or 60 Hz transformer. Thus, there is a need in UPS systems to maintain the integrity of the neutral conductor of the AC utility power, as well as the need to eliminate the 50 or 60 Hz transformer thereby actually reducing the overall cost, size and weight of such UPS systems.